The present invention relates to the field of gas monitoring and dosimetry in and, more particularly, to the field of passive dosimetry of hazardous gases, and concentration of ambient contaminants in the air.
Monitoring and sensing, also known as dosimetry, of hazardous gas concentrations is of considerable importance in the protection of employees of industrial plants and, more generally, the protection of civilian populations surrounding chemical operations and the protection of military personnel exposed to hazardous gas environments.
Numerous technologies have been developed for the estimation of what is term the time weighted average (TWA) gas concentration and for the estimation of gas exposure levels. The better known, and most important, of the existing methods of this type are briefly set forth below.
1. Bubbling of a known quantity of air through an absorbing solution and measuring concentrations of its reaction products in the solution. PA1 2. Passing a known quantity of gas through a column with a solid adsorbent which either changes color or is de-absorbed in a subsequent step, with the quantity of the de-adsorbed gas being determined. PA1 3. Adsorption of gas onto an activated carbon bed by means of a plastic material with apertures, and measuring the quantity of adsorbed gas over a known period of time. PA1 4. Absorption of gas into a solution and measuring the concentration of its reaction products on a continual basis, for example, through the use of an electrochemical cell. PA1 5. Measuring the change in electrical properties of surfaces of solid state devices after contaminant gases have been adsorbed by them. PA1 6. Measuring the length of color-stain developed in an open-end tube filled with a chromophore. PA1 7. Using a diffusion-barrier based passive sampler with a subsequent analysis employing spectrometric, electrochemical or chromatographic methods.
Commercially available gas dosimeters employing the techniques described above are generally designed for collecting ambient gas samples in the workplace and then, in a subsequent step, an employee-carried dosimeter is analyzed by an appropriate analytical method or instrument. Typically, each dosimeter is designed for a particular gas and, therefore, a different analytical method is required for each gas. Moreover, commercially available gas monitoring devices which employ the above methods are of high cost. Therefore, there has been, and currently exists, a need for economical gas monitoring techniques which is suitable to relatively wide range of gas monitoring situations.
The present invention is of a gas diffusion type and therefore, most closely resembles the prior art of Paragraph Number 3 above. More particularly, the present invention relates to a zero diffusion path gas dosimeter used in measuring the TWA gas concentration. An auxiliary instrument is contained within an enclosure adapted for selectable attachment and detachment to a worker which, both prior and subsequent to use is acted upon according to steps of the inventive method.
The prior art, as known to the inventor herein, is best reflected in U.S. Pat. Nos. 3,661,027 (1972) to Smith; U.S. Pat. No. 4,772,560 (1988) to Attar; and my own Czechoslovakia Patent No. 245,837.
The instant invention is also an improvement with respect to colormetric gas dosimeter reflected in U.S. Pat. Nos. 4,783,316 (1988) and 4,844,867 (1989) in which the measurement reaction products occurs within an instrument attached to the worker.